Vibrator inverter system



so) 33 TO SOURCE 3 m 43 2| VOLTAGE 9i 38 y 1942- M. A. EDWARDS 2,284,407

VIBRATOR INVERTER SYSTEM Filed May 271 i939 Inventor: Mar-tin A.E wards,

Patented May 26,1942

VIBRATOR INVERTER SYSTEM Martin A. Edwards, Schenectady, N. Y., assignor to General Electric Company, a corporation oi.

New York Application May 27, 1939, Serial No. 276,212

4 Claims.

My invention relates to vibrator inverter systems for supplying alternating current load circuits from a direct current source such as a storage battery. The invention relates particularly terially higher efiiciency than lamps heretofore employed. These newer type lamps operate on alternating current and are preferably energized from the train batteries through inverter equipment of the vibrating switch type.

Difficulties have been encountered, however, in utilizing inverters of this type in connection with train illumination equipment by reason partially of the wide variations in battery voltage, which in the case of the iron-nickel battery, for example, ranges between approximately 27 volts and 43 volts for a battery rated normally at 32 volts. The battery voltage variations have tended to cause variations in amplitude of the inverter vibrating switch element and thereby to impair the operation of the inverter system. Further, the battery voltage variations have been accompanied byunduly wide variations in the inverter alternating output voltage and in the current flowing in the lamps.

Di fiiculties in utilizing inverters of the vibrating switch type in connection with train illumination have also been encountered at the vibrating switch contacts, which because of the relatively large currents employed are commonly,

preferably so arranged that two or more contacts carry current in parallel. By reason of unequal distribution of the current flowing through the paralleled contacts, heating and burning have occurred at those of the contacts which were overloaded.-

It is an object of the invention to provide an improved vibrator inverter system, particularly for train illumination use, of high efliciency and of a high degree of reliability.

It is a further object to provide in a vibrator inverter system supplied from a varying voltage source, means responsive to the supply voltage variations to maintain substantially constant the 55 amplitude of vibration of the vibrating element of the inverter.

It is another object to provide, in a system comprising alternating current load circuits supplied from a source of varying direct voltage through a vibrator inverter, means responsive to the voltage variations of the supply source to limit to a desired degree the corresponding variations in the alternating output voltage of the inverter and in the current flowing in the load circuits.

It is a further object to provide, in a train lighting system comprising lamps of the fluorescent type supplied through a vibrator inverter from the train-lighting storage battery, means associated with the lamp circuit to limit to a substantial degree the varying of the current flowing in the lamps as the voltage of the battery varies.

In accordance with my invention, variations in amplitude of vibration of the vibrating switch element, or reed, as the battery voltage varies are prevented by so arranging the driving coil for the vibrating reed that, as the battery voltageincreases, the core of the driving coil saturates, the driving force exerted on the reed by the driving coil thereby tending to remain constant.

Unduly wide'variations in the alternating output voltage and in the current drawn by the lamps, as the battery voltage varies, are prevented in accordance with the invention by employing two types of lamp circuits, one in which the current is largely limited by capacity and the other in which the current is limited by inductance. By proper proportioning of the magnetic circuits of the two types of lamp units, the power factor of the system is caused to approach unity as the battery voltage increases whereby a better regulation 9f the alternating voltage of the inverter is obtained and at the higher battery voltages the lamps are prevented from operating at too high a'current value.

Heating and burning of contacts due to unequal distribution of. current through banks of paralleled contacts in the vibrator are prevented in accordance with the invention by the provision of small resistances in series with the contacts, or-the equivalent, whereby the currents through the paralleled contactsare equalized, the resistance loss, however, introduced by the resistances being so small that the overall efficiency of the inverter is aifected to a negligible degree.

The novel features which are considered to be characteristic of my invention are set forth with particularity in the appended claims. My invensentation of enlarged scale of the of the input terminals,

battery, for example,

tion itself, however, and method of operation objects and advantages understood by reference to the following description taken in connection with the accompanying drawing wherein Fig. l is a diagrammatic reprean illumination system embodying my invention, and Figs. 2 and 3 are, respectively, cross-sectional and side elevational views on an vibrator driving coil and a portion of the vibrating reed of the inverter included in the system illustrated in Fig. 1.

In Fig. 1 the numeral l designates a vibrator inverter, preferably of a series type heretofore proposed, including input terminals II and I2 both as to its-organization together with further connected to a source of varying direct voltage which in the present embodiment is a storage battery. and I6 connected in series across the input terminals, and a vibrator device or vibrating switch |6-. I'he latter device includes a-vibratile element carrying two banks of fixed contacts 20, 2| and 22, 23 on opposite sides of the movable contacts, a tip or armature element 24 at the free end of the vibratile element I1, and a magnetic element 26 to drive the vibratile element l1 including a core member 26 mounted adjacent the armature 24 and an energizing coil 21 connected between one as H, and the vibratile element H, the latter being connected through the primary winding of output transformer H to the midpoint 26 of the series connected condensers l4 and I6. A limiting or ballast resist ance 29 is connected in series with the energizing coil 21 of magnetic element 26. The two banks of paralleled fixed contacts 20, 2| and 22, 23 are connected respectively to the opposite input terminals II and I2. A second set of condensers 36 and 3| similar to condensers l4 and I6 may be provided, adapted to be connected respectively in parallel with the latter by a relay 32 responsive to voltage variations of the input voltage source. In order to lessen arcing at the contacts upon closing of the vibrating switch I6, non-linear reactors 33 and 34 are preferably provided in series respectively with the banks of fixed contacts, the reactors providing a period of low current value thereof may best be 1 an output transformer l3, condensers |4 a bank of movable contacts l3 and H,

two contacts each, the series resistance for the contacts may take the form of two resistors, as shown, one connected between contacts the other connected between contacts 22 and 23.

Variation of the load current to an undesirable degree in the output circuit of the inverter as the direct input voltage varies, is prevented, in a manner to be explained hereinafter, by providing lamp circuits in pairs, one lamp of a pair being capacitively and the other inductively ballasted, two of these lamp circuits, 36 and '31 which constitute one pair of the total load, being shown in the drawing. Each of the circuits 36 and 31 comprises a lamp of the fluorescent type which, as is well known, requires for the starting of the discharge therein a higher voltage than that required to maintain the discharge after it has been started.

Circuits of the type designated by the numeral 36 are disclosedin my Patent No. 2,170,447, August 22, 1939. In circuit 36 the lamp 46 is connected to the'output circuit of inverter |0 through ballast devices comprising the reactor 41 and the capacitor 46 in series. The reactor 41 and capacitor 46 constitute a circuit which is in a condition of partial resonance, that is the inductance and capacitance of the latter circuit are such that the circuit is partly tuned or, in other words,

is operated off the resonance peak. Connected across the lamp 46 is a second with the electrodes 60and 6|. In accordance with my present invention the reactor 41 is of the non-linear type for a purpose to be described when the contacts close the circuit. Such reactors are disclosed in combination with vibrator inverter circuits in application Serial No. 113,581, filed December 1, 1936, and assigned to the same assignee as the present application. Alternating voltage is impressed through a load circuit line 36 on a plurality of lamp circuits, two of which, 36 and 31 are shown in the figure.

In order to limit the variations vibration of the switch element H as the input voltage varies, as shown in detail in Figs. 2 and 3 in accordance with the invention a bridge gap 36 is provided in the main leg 39 of the magnetic driving unit 26 in such manner that as the voltage of the input source such as a train lighting increases, the small remaining' sections, 40 and 4|, at the gap 33, saturate, the saturation of the sections 40 and 4| being equivalent to increasing the air gap between the reed tip or armaturels and the core 26 as'the voltage impressed on the driving coil 21 increases.

In order to divide equally the current flowing through the paralleled contacts of the vibrating switch I6, small resistances 42 to 46 (Fig. 1) are connected respectively in series with the fixed contacts 26 to 23. In the present embodiment wherein the banks of fixed contacts comprise only in amplitude of hereinafter, being so arranged that the core 62 tends to saturate as the current through the reactor increases, thereby reducing the inductance of the partially resonant circuit with increase of current therein.

Circuits of the type designated by the numeral 31 are disclosed in my Patent No. 2,170,449, August 22, 1939. In circuit 31 the lamp "is connected atone of its electrodes, 64, to one of the output circuit lines 36 through a ballast reactor 66. At a point intermediate the ends of this reactor, shown by way of example as the mid-point thereof, is a tap 66 and connected between this tap and the other lamp electrode 61 and the other of the output circuit lines is a branch circuit constructed to have a leading power factor and comprising a reactor 66 and a capacitor 69, the latter reactor and capacitor being arranged in series. The reactor 66 thus constitutes a step-up transformer of which that part of the winding between the lines 36 and the point 66 is the primary and the entire winding is the secondary.

when starting the 63 and 6| are'proand respectively in inductive relation with reactor 66 and the section 62 of reactor 66 to which the electrode 64 is connec In operation of the illumination system illustrated in the drawing, varying direct voltage from the railway train storage battery or other similar source connected to input terminals ll 63, preferably coils and I2 being supplied to the inverter It, the

26 and2l,"

reactor 43 in series To assist in preliminary. heating of the electrode 64 -lamp vided in series with the electrode 64 Movable contacts l6 and ing to vary correspondingly with the input voltage variations, in the load circuit supply lines 35.

In case the direct supply voltage rises to a predetermined high value, relay 32 operates to connect the auxiliary condensers 36 and 3| in parallel respectively with condensers l4 and I5.

At low and normal values of direct input voltage impressed on the driving coil 21 of magnetic element 25, the current in the latter coil is of such value that the core 26 is not saturated. The flux in the core under these conditions is of proper value to maintain a desired amplitude of oscillation of vibratile element l1. When the input voltage rises causing the current in coil 21 to rise, the increasing degree of saturation of the core tends to prevent the rise of flux in the core.

Therefore under conditions of high voltage impressed on coil 21 and correspondingly high current therein, by the provision-of the saturable core 26 the amplitude of vibration of vibrator element 11 is maintained at approximately its proper normal value. When the core 26 saturates as described, due to the excessive voltage 2 impressed upon the driving coil 21, and the impedance of the magnetic element drops correspondingly, the extra voltage in the driving coil circuit appears across the ballast resistor 29.

Whenvibratile element 11 assumes its closed 30 positions to cause the parallel movable contacts, l8 and 19 in the present embodiment, to move into momentary engagement with the banks of paralleled fixed contacts, the effect of differences in resistance to the flow of current at the several contact pairs in engagement is lessened to a suitable degree or made practically negligible by the resistors, as 42 to 45, which are connected respectively in series with the fixed contacts. In practice I have found that to cause the several paralleled pairs of contacts to divide the load properly, the resistance values of the resistors required in series with the contacts are relatively small.

At starting of the load circuit 36, the capacitor 48 and the reactor 41 constitute a circuit which is partly tuned, or in other words is operated actor 53 and the capacitor 53. Having started,

the lamp 53 continues to operate, with the reactor 55 in combination with reactor 58 and capacitor 56 as the effective ballast. The lamp 53 and that part of the reactor 55 between the tap 56 and the electrode 54 now form a shunt around the branch circuit comprising the reactor 58 and the capacitor 53 so that the current in the latter branch circuit ismaterially reduced but, nevertheless, is of such value that the capacitor 53 changes the power factor of the load circuit 31 to such an extent that the current drawn from the supply circuit 35 by load circuit 31 is less lagging than would otherwise be the case. r

Load circuits 36 and 31 after starting now operate in parallel, the power factor in circuit 36 being leading and the power factor in circuit.

being lagging. The constants of these paralleled l circuits are such that the resultant power factor, or power factor of the total load, is preferably lagging under all conditions of the varying impressed voltage.

Let it be assumed first that the direct voltage impressed on the inverter input terminals II and I! from the train lighting storage battery or other similar source has its minimum value or a low range of values. Under these conditions, the ballast elements, respectively capacitive and inductive, of. the circuits 36 and 31 may have such values that the resultant power factor is and capacitor 48 thus decreases, the latter ciroif the resonance peak. As a result of this con-' dition the voltage across reactor 49 at starting,

and hence the voltage across the electrodes 56 50 and 5| of the lamp 46 is raised considerably above that of the output circuit 35 of the inverter I0 and is sufficient to start a discharge in this lamp. As soon as the discharge starts, the reactor 49 is substantially short circuited by the lamp inasmuch as the impedance of the lamp is materially less than that of the latter reactor. The lamp 46 continues to operate therefore on the circuit comprising substantially only the reactor 41 and capacitor 48. Since the reactance provided by the capacitor 48 predomi-w nates over the reactance provided by the reactor 41 the lamp 46 operates with capacitive ballast and hence the load circuit 36 draws a leading current from the supply circuit 35 of inverter l0.

At starting of the load circuit 31, the circuit constituted by that portion of the reactor forming an autotransformer, together with the reactor 58 and the capacitor 53 is partly tuned 70 actor 55 due to the leading current drawn 75 cuit therefore becomes still more capacitive. The resultant power factor due to the capacitive ballast of circuit 36 and the inductive ballast of circuit 31 therefore becomes less lagging, or in other words, approaches closer to unity. At the same time, by reason principally of the constant arc drop which is characteristic of the lamps employed, the power factor of circuit 31 becomes, as the impressed voltage rises, slightly less lagging thereby contributing to causing the resultant power factor of the total load to become less lagging. The eil'ect of the above described ballast means of circuits 36 and 31 may be such that as the impressed direct voltage rises to its higher range the resultant power factor, ap-

proaching imity from its approximately percent value under low voltage conditions, becomes approximately per cent. I have found that by arranging the load on inverter Ill in pairs of lamp circuits respectively capacitively and inductively ballasted such as circuits 36 and 31, and providing means to cause the resultant power factor of the load to approach unity with rise Under these latter condigas discharge devices. 7

Subject matter of the present application directed to structure of a vibrator inverter is claimed in a divisional application, Serial No. 871,448, filed December 23, 1940.

My invention has been described herein in a particular embodiment for purposes of illustration. It is to be understood, however, that the invention is susceptible of various changes and modifications and that by the appended claims I intend to cover any such modifications as fall within the true spirit and scope of my invention.

What I claim as new and desire to secure by Letters Patent of the United States is:

1. In combination, a source of unidirectional voltage varying over a substantial range between predetermined minimum and maximum values, a vibrator inverter connected to said source, a load circuit connected to said inverter comprising an electric discharge device, ballast means to cause said device to operate with a leading power factor of maximum value at said minimum'voltage and of minimum value at said maximum voltage, 'a second load circuit connected to said inverter comprising a second electric discharge device, and ballast means to cause said second-named device to operate with a lagging power factor of minimum value at said minimum voltage and of maximum value at said maximum voltage, whereby the resultant power factor of said load circuits increases when said voltage rises from 'said minimum to said maximum value.

' 2. In combination, a source of unidirectional voltage varying over a substantial range between said maximum voltage, whereby the. resultant power factor of said circuits increases when said voltage rises from said minimum to said maximum value to approach unity as the voltage of comprising a second electric discharge device,

predetermined minimum and maximum values,

a vibrator inverter connected to said source, a load circuit connected to said inverter comprising an electric discharge device, capacitive ballast means'in series therewith to cause said device to operate with a leading power factor, said ballast means including a capacitor and a nonlinear reactor adapted to saturate upon increase of current therethrough to cause said power factor to change froma maximum value at said minimum voltage to .a minimum value at said maximum voltage, a second load circuit connected to said inverter comprising a second electric discharge device, and inductive ballast means to cause said second device to operate with a lagging power factor of minimum value at said minimum voltage and of maximum value at and inductive balla'st means to cause said second device to operate with a lagging power factor increasing when said voltage rises from said minimum to said maximum value, said inductive ballast means comprising a reactor in series with said second device and a branch circuit in parallel therewith, said branch circuit including a reactor and a capacitorv in series and having a leading power factor, whereby the resultant power factor of said load circuits increases when said voltage rises from said minimum to said maximum value.

4. In combination, a source of unidirectional voltage varying between predetermined minimum and maximum values, a vibrator inverter connected to said source, a'load circuit including. a lamp connected to said inverter, capacitive bailast means in series with said lamp to cause said circuit to operate with a leading power factor, said ballast means including a capacitor and a non-linear reactor adapted to saturate upon increase of current therethrough to cause said power factor-.to decrease when said voltage rises from said minimum to said maximum value, a, second load circuit in parallel with said first load circuit and including a second lamp, and inductive ballast means to cause said second circult to operate with a lagging power factor increasing when said voltage rises from said minimum to said maximum value, said inductive ballast means comprising a reactor in series 

